Carbon materials derived from cellulosic materials and/or regenerated cellulosic materials as the raw materials thereof are used in a variety of fields. Currently, such carbon materials are used in the form of a fiber, particle, or mass in many cases, while there are very few application examples of carbon materials in a thin planar form such as film or membrane. Examples of such a planar-form carbon material include conductive carbon paper or cloth, which is a carbon fiber product used as a material for a gas diffusion layer in an electrode of a fuel cell and is quite expensive.
It is appreciated that heating a cellulosic material at high temperature in an inert gas results in dehydration and depolymerization of the cellulosic material through pyrolysis, induces complex degradation reactions, which include generation of low-molecular-weight materials such as levoglucosan, and the like; as well as it produces CO, CO2, H2O, and other volatile gases, and finally leaves a black material composed mainly of carbon (Non-patent Documents 1 and 2).
Due to such features of pyrolysis, it is quite difficult for a cellulosic material having a form of, for example, film to retain the shape thereof and the obtained carbon material is very fragile.
Recently, a technology which takes advantage of the properties of cellulosic materials has been reported, in which network-type and sheet-type carbon materials, which have large specific surface areas and novel configurations and varied graphitization rates, can be obtained in high yield from a gel-like bacterial cellulose produced by a bacteria (Patent Document 1). Moreover, recently, the inventors have reported that a carbon material which retains the shape of a cellulosic material can be provided by treating the cellulosic material with a halogen or a halide prior to heat treatment (Patent Document 2).